Process for producing 2,3,3,3-tetrafluoropropene

ABSTRACT

The instant invention relates to a process and method for manufacturing 2,3,3,3-tetrafluoropropene by dehydrohalogenating a reactant stream of 2-chloro-1,1,1,2-tetrafluoropropane that is substantially free from impurities, particularly halogenated propanes, propenes, and propynes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is Continuation of U.S. application Ser. No.14/643,668, filed Mar. 10, 2015 which application is a Continuation ofU.S. application Ser. No. 13/281,063, filed Oct. 25, 2011, (now U.S.Pat. No. 8,975,454, issued Mar. 10, 2015), which application is relatedto and claims the priority benefit of U.S. provisional application No.61/414,074 filed Nov. 16, 2010, the contents of which are incorporatedherein by reference.

U.S. application Ser. No. 13/281,063 is also a continuation-in-part ofU.S. application Ser. No. 12/510,740, filed Jul. 28, 2009, which claimsthe priority benefit of U.S. provisional application No. 61/085,141,filed Jul. 31, 2008, the contents each of which are incorporated hereinby reference.

FIELD OF THE INVENTION

This invention relates to a novel method for preparing fluorinatedorganic compounds, more particularly to a method for preparingfluorinated olefins, and even more particularly to a method forproducing 2,3,3,3-tetrafluoropropene (HFO-1234yf).

BACKGROUND OF THE INVENTION

Hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including2,3,3,3-tetrafluoropropene (HFO-1234yf)), are now known to be effectiverefrigerants, fire extinguishants, heat transfer media, propellants,foaming agents, blowing agents, gaseous dielectrics, sterilant carriers,polymerization media, particulate removal fluids, carrier fluids,buffing abrasive agents, displacement drying agents and power cycleworking fluids. Unlike chlorofluorocarbons (CFCs) andhydrochlorofluorocarbons (HCFCs), both of which potentially damage theEarth's ozone layer, HFOs do not contain chlorine and, thus, pose nothreat to the ozone layer. HFO-1234yf has also been shown to be a lowglobal warming compound with low toxicity and, hence, can meetincreasingly stringent requirements for refrigerants in mobile airconditioning. Accordingly, compositions containing HFO-1234yf are amongthe materials being developed for use in many of the aforementionedapplications.

One known precursor used to prepare HFO-1234yf is2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb). Indeed, there arenumerous gas phase reactions that are known for the production ofHFO-1234yf by HCFC-244bb dehydrochlorination. U.S. Pub. No. U.S.2007/0197842, for example, teaches the synthesis of HFO-1234yf throughgas phase HCFC-244bb dehydrochlorination in the presence of a carbon-and/or metal-based catalyst (e.g. nickel or palladium based catalysts).U.S. Pub. No. U.S. 2009/0043136 also teaches the preparation ofHFO-1234yf through gas phase HCFC-244bb dehydrochlorination in thepresence of a catalyst selected from the group consisting of (i) one ormore metal halides, (ii) one or more halogenated metal oxides, (iii) oneor more zero-valent metals/metal alloys, or (iv) a combination of two ormore of the foregoing.

While the foregoing reactions disclose processes having relatively highconversion levels, such reactions are not without disadvantages. Asillustrated herein, known processes for the production of HCFC-244bboften produce only about a 90% yield. Thus, the remainder of the productstream includes undesirable by-products and raw materials. Theseby-products and raw materials are surprisingly shown herein to have adetrimental impact on the ability to produce high purity HFO-1234yf whenused in connection with one or more of the applications mentioned above.As a result, they reduce product yields and increase associated costs.

Based on the foregoing, there is a continuing need for an improvedprocess of preparing high purity HFO-1234yf from HCFC-244bb. The instantinvention and the embodiments presented herein addresses at least thisneed.

SUMMARY OF INVENTION

The present invention relates, in part, to the surprising discoverythat, during the dehydrochlorination of HCFC-244bb to form2,3,3,3-tetrafluoropropene (HFO-1234yf), even a small amount of certainimpurities in the reactor feed, particularly the HCFC-244bb feed stock,have a significant negative impact on (a) the ability to purify thefinal HFO-1234yf product; (b) the stability of the dehydrochlorinationcatalyst; and/or (c) the resulting reaction product stream. The instantinvention provides methods of improving the production of high purityHFO-1234yf by substantially purifying the HCFC-244bb feed prior todehydrohalogenation.

In one aspect, the instant invention relates to a process for making2,3,3,3-tetrafluoropropene and preferably high purity2,3,3,3-tetrafluoropropene by (a) providing a distillation inseparablefeed stream of 2-chloro-1,1,1,2-tetrafluoropropane and at least oneimpurity in an amount greater than about 500 parts per million; (b)treating the feed stream until it is substantially free from the atleast one impurity; and (c) dehydrohalogenating the2-chloro-1,1,1,2-tetrafluoropropane containing feed stream to produce2,3,3,3-tetrafluoropropene. In certain embodiments, the treated feedstream contains less than 5% total weight of impurities, less than 3%total weight of impurities, less than 1% total weight of impurities, orless than 0.5% total weight of impurities.

Reactant stream impurities may include any one or more compounds thatinhibit the ability to produce high purity 1234yf in high yields, thestability of the dehydrochlorination catalyst or otherwise have anegative impact on the resulting product stream (containing toxicimpurities). In one embodiment, such impurities include one or morecompounds of formula I:X_(a)C═CY_(b)—CZ₃   (I)wherein the bond between the first and second carbon atoms is denoted asbeing either a single, double or triple bond; a is 1, 2, or 3, and b is0, 1, or 2, and each individual X, Y, and Z are independently Cl, I, Br,F, or H, subject to the proviso that Formula I does not include2-chloro-1,1,1,2-tetrafluoropropane or 2,3,3,3-tetrafluoropropene.

In certain embodiments of formula I, the impurities may include one ormore compounds selected from the group halogenated propanes, halogenatedpropenes, or halogenated propynes. Such impurities include, but are notlimited to, one or a combination of 1,1,1,2,2-pentafluoropropane(HFC-245cb), 1,1,1,2-tetrafluoropropane (HFC-254eb),1,1,1,3-tetrafluoropropane (HFC-254fb), 3,3,3-trifluoropropene(HFO-1243zf), 2,3-dichloro-3,3-difluoropropene (HCFO-1232xf),2-chloro-3,3,3-trifluoropropene (HCFO-1233xf),1-chloro-3,3,3-trifluoropropene (HCFO-1233zd),1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd),chlorotetrafluoropropenes (HCFO-1224 isomers),1,2,3,3,3-pentafluoropropene (HFO-1225ye (cis and trans isomers)),1,3,3,3-tetrafluoropropene (HFO-1234ze (cis and trans isomers)), and3,3,3-trifluoropropyne.

Improved product purity and catalyst stability is obtained when suchimpurities are contained in the following amounts: from 0 to about 400part per million (ppm) of 3,3,3-trifluoropropene (HFO-1243zf), from 0 toabout 200 ppm of 2,3-dichloro-3,3-difluoropropene (HCFO-1232xf), from 0to about 200 ppm of 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), from0 to about 200 ppm 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), from 0to about 200 ppm 1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd), from0 to about 200 ppm chlorotetrafluoropropenes (HCFO-1224 isomers), from 0to about 200 ppm 1,2,3,3,3-pentafluoropropene (HFO-1225ye (cis and transisomers)), from 0 to about 200 ppm 1,3,3,3-tetrafluoropropene(HFO-1234ze (cis and trans isomers)), from 0 to about 200 ppm1,1,1,2,2-pentafluoropropane (HFC-245cb), from 0 to about 200 ppm1,1,1,2-tetrafluoropropane (HFC-254eb), from 0 to about 200 ppm1,1,1,3-tetrafluoropropane (HFC-254fb), and from 0 to about 200 ppm of3,3,3-trifluoropropyne. The foregoing amounts, however, are not limitingto the instant invention.

Methods of ensuring that the 2-chloro-1,1,1,2-tetrafluoropropanecontaining feed stream is substantially free from impurities include,but are not limited to, subjecting the feed stream to one or acombination of a photochlorination reaction, a hydrogenation reaction,distillation or a liquid-liquid extraction.

Accordingly, and in certain embodiments, the instant invention relatesto a method for removing the impurities from a2-chloro-1,1,1,2-tetrafluoropropane raw feed stock by (a) optionally,subjecting said 2-chloro-1,1,1,2-tetrafluoropropane raw feed stock to aphotochlorination process; and (b) purifying2-chloro-1,1,1,2-tetrafluoropropane feed to produce a substantially pure2-chloro-1,1,1,2-tetrafluoropropane feed. The photochlorination processmay include, but is not limited to, reacting impurities with chlorine(Cl₂) in the presence of electromagnetic radiation, which may includeultraviolet light. While a multitude of reaction conditions may be used,in one embodiment, the reaction proceeds in a gas phase or a liquidphase and at a temperature of about 0° C. to about 50° C.

The step of purifying said raw feed stock may include any purificationor separation technique known in the art for extracting2-chloro-1,1,1,2-tetrafluoropropane from impurities contained withineither the raw feed stock or the photochlorinated feed stock. In oneembodiment, the purification method includes distillation. To this end,the raw feed stock is distilled using one or more distillation columnsor packed towers. While distillation may occur at atmospheric pressure,super-atmospheric pressure or under vacuum, in certain embodiments it isconducted at a pressure of less than about 300 psig. It may also beconducted at a temperature from about −10° C. to about 90° C. Again, theinstant invention is not so limiting and may include other purificationmethods such as a liquid-liquid extraction, which may be used alone orin combination with other extraction methods.

In further embodiments, the instant invention relates to a method forremoving the impurities from a 2-chloro-1,1,1,2-tetrafluoropropane feedby (a) subjecting said 2-chloro-1,1,1,2-tetrafluoropropane feed to ahydrogenation process; and (b) purifying the2-chloro-1,1,1,2-tetrafluoropropane feed to produce a substantially pure2-chloro-1,1,1,2-tetrafluoropropane feed. The hydrogenation processincludes, but is not limited to, reacting impurities with hydrogen (H₂)in the presence of one or more catalysts. Such catalysts may include oneor a combination of Pt, Pd, and Ni, either un-supported or supported onan inert support. In the latter context, support substrates may includeone or more of the following: activated carbon, alumina, different metaloxides, zeolites, alumosilicates, and molecular sieves. While amultitude of reaction conditions may be used, in one embodiment, thehydrogenation reaction is performed in a gas phase or a liquid phase andat a temperature from about 50° C. to about 400° C.

The step of purifying said raw feed stock may include any purificationor separation technique known in the art for extracting2-chloro-1,1,1,2-tetrafluoropropane from impurities contained withineither the raw feed stock or the hydrogenated feed stock. In oneembodiment, the purification method includes distillation. To this end,the raw feed stock is distilled using one or more distillation columnsor packed towers. While distillation may occur at atmospheric pressure,super-atmospheric pressure or under vacuum, is conducted at a pressureof less than about 300 psig in certain embodiments. It may also beconducted at a temperature from about −10° C. to about 90° C. Again, theinstant invention is not so limiting and may include other purificationmethods such as a liquid-liquid extraction, which may be used alone orin combination with other extraction methods.

In further embodiments, the instant invention relates to a process forproducing high purity 2,3,3,3-tetrafluoropropene by (a) providing a feedstream comprising 2-chloro-1,1,1,2-tetrafluoropropane and at least oneimpurity; (b) subjecting the raw feed stock to either or both aphotochlorination process and a hydrogenation process to form a modifiedfeed stream; (c) purifying 2-chloro-1,1,1,2-tetrafluoropropane from theraw feed reaction stream or modified feed stream to produce asubstantially pure 2-chloro-1,1,1,2-tetrafluoropropane feed stock; and(d) dehydrohalogenating said substantially pure2-chloro-1,1,1,2-tetrafluoropropane feed stock. Non-limiting methodsassociated with each of the foregoing steps are provided herein.

Additional embodiments and advantages to the instant invention will bereadily apparent to one of skill in the art based on the disclosureprovided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the 244bb conversion over MgF₂ catalyst with89.7%244bb/7.3%1233xf/3.0% others feed (450° C., 1 atm, 6 g-organic/h)

FIG. 2 illustrates the stability of 10 wt % CsCl/MgF2 Catalyst.

FIG. 3 illustrates 244bb conversion as a function of time on streamduring 244bb dehydrochlorination in ¾″ Inconel 625×0.035″ reactor (480°C.,˜25 psig)

DETAILED DESCRIPTION OF THE INVENTION

As provided herein, the instant invention relates to the surprisingdiscovery that, during the dehydrochlorination of HCFC-244bb to form2,3,3,3-tetrafluoropropene (HFO-1234yf), even a small amount of certainimpurities in the reactor feed, particularly the HCFC-244bb feed stock,have a significant negative impact on (a) the ability to purify thefinal HFO-12334yf product; (b) the stability of the dehydrochlorinationcatalyst; and/or (c) the resulting reaction product stream. Accordingly,the instant invention, at least in part, relates the methods ofimproving the production of high purity HFO-1234yf by substantiallypurifying the HCFC-244bb reactor feed.

As used herein, the term “impurity,” “impurities,” or “unsaturatedimpurities” may include any chemical compound, particularly ahalocarbon-based compound, within the HCFC-244bb stream that interfereswith the stability of the dehydrochlorination catalyst or otherwisereduces the conversion rate and/or selectivity of HCFC-244bb toHFO-1234yf. In particular embodiments, such impurities may berepresented by the following formula I:X_(a)C═CY_(b)—CZ₃   (I)wherein the bond between the first and second carbon atoms is denoted asbeing either a single, double or triple bond; a is either 1, 2, or 3,and b is either 0, 1, or 2, depending on the number of atoms necessaryto satisfy the valence requirements of each respective carbon atom, andwherein each individual X, Y, and Z are independently Cl, I, Br, F, orH. The foregoing formula is subject to the proviso, however, that itdoes not include either HCFC-244bb or HFO-1234yf.

In another embodiment, the impurities of the instant invention and offormula I include, but are not limited to, halogenated propanes,halogenated propenes, or halogenated propynes and combinations thereof.Exemplified halogenated propane impurities include, but are not limitedto, 1,1,1,2,2-pentafluoropropane (HFC-245cb), 1,1,1,2-tetrafluoropropane(HFC-254eb), 1,1,1,3-tetrafluoropropane (HFC-2541b), and combinationsthereof. Exemplified halogenated propenes include, but are not limitedto, 3,3,3-trifluoropropene (HFO-1243zf),2,3-dichloro-3,3-difluoropropene (HCFO-1232xf),2-chloro-3,3,3-trifluoropropene (HCFO-1233xf),1-chloro-3,3,3-trifluoropropene (HCFO-1233zd),1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd),chlorotetrafluoropropenes (HCFO-1224 isomers),1,2,3,3,3-pentafluoropropene (HFO-1225ye (cis and trans isomers)),1,3,3,3-tetrafluoropropene (HFO-1234ze (cis and trans isomers)), andcombinations thereof. An exemplified halogenated propyne includes, butis not limited to, 3,3,3-trifluoropropyne.

As provided herein, one aspect of the instant invention is removal ofsuch impurities to form a substantially pure HCFC-244bb reaction streamor HCFC-244bb that is substantially free from impurities. As used hereinthe terms “substantially pure” or “substantially free” refer to theHCFC-244bb reactant stream having an amount of one or more impuritiesremoved therefrom so as to improve the ability to produce high purityHFO-1234yf, improve yields, and decrease associated costs. In oneaspect, the impurities are “substantially free” in that they domeasurably impede the conversion of 244bb to 1234yf. In one embodiment,the final HCFC-244bb stream contains not more than about 5% total weightof the impurities. In further embodiments, it refers to the HCFC-244bbreactant stream having not more than 3% total weight of the impurities.In even further embodiments, it refers to the HCFC-244bb reactant streamhaving not more than 1% total weight of the impurities. In even furtherembodiments, it refers to the HCFC-244bb reactant stream having not morethan 0.5% total weight of the impurities.

In even further embodiments, final 1234yf product purity and catalyststability is obtained when such impurities in the final reactant feedstream are reduced to the following amounts: from 0 to about 400 partper million (ppm) of 3,3,3-trifluoropropene (HFO-1243zf), from 0 toabout 200 ppm of 2,3-dichloro-3,3-difluoropropene (HCFO-1232xf), from 0to about 200 ppm of 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), from0 to about 200 ppm 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), from 0to about 200 ppm 1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd), from0 to about 200 ppm chlorotetrafluoropropenes (HCFO-1224 isomers), from 0to about 200 ppm 1,2,3,3,3-pentafluoropropene (HFO-1225ye (cis and transisomers)), from 0 to about 200 ppm 1,3,3,3-tetrafluoropropene(HFO-1234ze (cis and trans isomers)), from 0 to about 200 ppm1,1,1,2,2-pentafluoropropane (HFC-245cb), from 0 to about 200 ppm1,1,1,2-tetrafluoropropane (HFC-254eb), from 0 to about 200 ppm1,1,1,3-tetrafluoropropane (HFC-254fb), and from 0 to about 200 ppm of3,3,3-trifluoropropyne.

The methods of removing the impurities from the HCFC-244bb reactant feedmay include one or a combination of methods that are known in the art.In one embodiment, the methods include the following steps: (a)providing a raw feed stock comprising HCFC-244bb and one or moreimpurities; (b) subjecting said raw feed stock to a photochlorinationprocess or hydrogenation process to produce a modified feed stockcomprising a reduced amount of at least one of said impurities comparedto said raw feedstock, preferably a reduced amount of the unsaturatedhalocarbon impurities compared to said raw feed stock; (c) purifyingsaid raw feed stock or said modified feed stock to produce asubstantially pure feed stock via an extraction or separation technique,wherein said high purity feed stock comprises relatively fewerimpurities when compared to said raw feed stock or said modified feedstock; (d) subjecting said substantially pure feed stock to conditionseffective to dehydrochlorinate at least a portion of said HCFC-244bb toproduce a reaction product comprising relatively more HFO-1234yf, ascompared to a reaction product using a feed that is not substantiallyfree of impurities. To this end, the substantially pure reactant feed iseffective to produce a final product comprising a majority of HFO-1234yfand a minority, if any, of impurities.

The initial step of producing HCFC-244bb may be accomplished using oneor more methods that are known in the art. One such non-limiting methodis the hydrofluorination of HCFO-1233xf, such as that disclosed in U.S.application Ser. No. 12/338,466, the contents of which are incorporatedherein by reference. To this end, catalysts are employed to enhance thesingle-pass conversion of HCFO-1233xf to HCFC-244bb via HF additionacross the double bond of HCFO-1233xf. Catalysts for performing thisstep may include, but are not limited to, SbCl₃, SbCl₅, SbF₅, TiCl₄,SnCl₄, Cr₂O₃, and fluorinated Cr₂O₃. The hydrofluorination process maybe carried out in a vapor phase or a liquid phase.

In vapor-phase hydrofluorination, HF (hydrogen fluoride gas) is fedcontinuously through the catalyst bed. After a short time with only theHF feed stream, HCFO-1233xf is fed continuously through the catalyst bedat a ratio of about 1:1 to about 1:30 and preferably from about 1:2 toabout 1:15 (HCFO-1233xf/HF mole ratio). The reaction between HF andHCFO-1233xf is carried out at a temperature from about 30° C. to about400° C. (preferably from about 100° C. to about 300° C.) and at apressure of about 5 psia to about 200 psia (pounds per square inchabsolute) (preferably from about 30 psia to about 175 psia). Thecatalyst may be supported on a substrate, such as on activated carbon,or may be unsupported or free-standing. In addition to activated carbon,useful catalyst supports include: alumina, fluorinated alumina, aluminumfluoride, alkaline earth metal oxides, fluorinated alkaline earthmetals, zinc oxide, zinc fluoride, tin oxide, and tin fluoride. Thecatalyst may (or may not) have to be activated with anhydrous hydrogenfluoride HF (hydrogen fluoride gas) before use depending on the state ofthe catalyst.

In liquid phase hydrofluorination, the catalyst is charged in a liquidform to a reactor and optionally activated with HF. The activatedcatalyst is then heated to the desired reaction temperature of about 30°C. to about 200° C. (preferably from about 50° C. to about 120° C.) andthe pressure is kept between about 15 psia to about 200 psia (preferablyfrom about 50 psia to about 175 psia). After a short time with only HFfeed, a HCFO-1233xf feed stream is fed continuously through the catalystat a ratio of about 1:1 to about 1:30 and preferably about 1:2 to about1:15 (HCFO-1233xf/HF mole ratio). If necessary, the catalyst can be keptactivated by the continuous or batch addition of Cl₂ or a similaroxidizing agent.

The hydrofluorination reaction is preferably carried out to attain aconversion of about 70% or, preferably, about 90% or more. Conversion iscalculated by the number of moles of reactant (HCFO-1233xf) consumeddivided by number of moles of reactant (HCFO-1233xf) fed to the reactormultiplied by 100. The selectivity for HCFC-244bb attained is preferablyabout 60% or more and most preferably about 80% or more. Selectivity iscalculated by number of moles of product (HCFC-244bb) formed divided bynumber of moles of reactant consumed.

Hydrofluorination may be carried out in a corrosion-resistant reactionvessel. Examples of corrosion-resistant materials are Hastelloy, Nickel,Incoloy, Inconel, Monel and fluoropolymer linings. The vessel may have afixed catalyst bed, or contain liquid catalyst. If desired, inert gasessuch as nitrogen or argon may be employed in the reactor duringoperation.

The foregoing hydrofluorination steps are not necessarily limiting tothe instant invention, however, and may also include derivative oralternative methodologies that are otherwise known in the art.

Once HCFC-244bb is produced, but before it is fed into thedehydrohalogenation reactor, it is processed for the reduction ofreaction impurities using one or a combination of the methods providedherein. In certain embodiments, and prior to entering the HCFC-244bbdehydrochlorination reactor, the unsaturated impurities of theHCFC-244bb reactant feed are first converted, via a photochlorinationreaction, into corresponding saturated halogenated hydrocarbons havingincreased chlorine content. More specifically, in the photochlorinationreaction chlorine (Cl₂) reacts with the unsaturated impurities in thepresence of an electromagnetic source, such as an ultraviolet lightsource.

In one embodiment of the photochlorination process, electromagneticradiation, e.g. UV light, from a suitable source is directed through areactor wall to interact with the impurities contained therein. Thesource of light may be any one of a number of arc or filament lampsknown in the art. Quartz or borosilicate glass such as Pyrex glass maybe employed as transparent material to construct the portion of thereactor wall through which the light passes and enters the reactor. Thephotochlorination may be continuously carried out in the gas phase, inwhich starting materials are vaporized and contacted with chlorine vaporin a reaction zone. Although a wide range of chlorination reactionconditions are believed to be suitable, in certain preferred embodimentsthe reaction temperature is from about 0° C. to about 50° C.Alternatively or additionally, the chlorination may be carried out inthe liquid phase by feeding chlorine to a reactor containing startingmaterials, with it generally being preferred to control the reactiontemperature below the boiling points of the starting materials andproducts.

In alternative or additional embodiments, the unsaturated impurities areconverted, prior to entering the HCFC-244bb dehydrochlorination reactor,into corresponding saturated halogenated hydrocarbons having increasedhydrogen content, preferably via hydrogenation in which hydrogen (H₂)reacts with the unsaturated impurities in the presence of a catalyst. Inone embodiment of the hydrogenation process, a suitable catalyst is usedto facilitate the hydrogenation reaction. Non-limiting examples ofhydrogenation catalysts are Pt, Pd, Ni or mixtures thereof un-supportedor supported on inert support. The catalyst support may include, but isnot limited to, activated carbon, alumina, different metal oxides,zeolites, alumosilicates or molecular sieves.

The hydrogenation reactor can be made of any material of constructionknown in the art such as steel, stainless steel, or metal alloys, etc.It is preferable that the reactor is equipped with temperature andpressure control. The hydrogenation reaction may be continuously carriedout in the gas phase, in which starting materials are vaporized andcontacted with hydrogen gas in a reaction zone. Although a wide range ofhydrogenation reaction conditions are believed to be suitable, incertain preferred embodiments the reaction temperature is from about 50°C. to about 400° C. Alternatively or additionally, the hydrogenation maybe carried out in the liquid phase by feeding hydrogen to a reactorcontaining starting materials, with it generally being preferred tocontrol the reaction temperature below the boiling points of thestarting materials and products.

The feed stream, whether or not it was subjected to thephotochlorination and/or hydrogenation, is then treated with one or acombination of compound separation techniques, such as, but not limitedto, distillation and/or extraction. Although it is contemplated that awide range of separation conditions can be used in accordance with thepresent invention, in certain embodiments the HCFC-244bb raw materialsare distilled by passing through one or multiple standard distillationcolumns and/or packed towers, or the like, which may be provided atatmospheric pressure, super-atmospheric pressure or a vacuum.Preferably, though not exclusively, the pressure is less than about 300psig, more preferably less than about 150 psig and most preferably lessthan 100 psig.

The HCFC-244bb may be recovered as distillate by operating thedistillation column at from about −10° C. to about 90° C., preferablyfrom about 0° C. to about 80° C. While not limited thereto, multipledistillation columns may be preferred because of the presence of anazeotrope or azeotrope-like composition of HCFO-1233xf and HCFC-244bbthat is known to exist.

In alternative or additional embodiments, the HCFC-244bb stream may bepurified using extraction techniques that are known in the art. One suchextraction technique is a liquid-liquid extraction, where HCFC-244bb isextracted based on its known solubility in one or more solvents.

Using one or a combination of the foregoing extraction or separationtechniques, the HCFC-244bb reactant feed is substantially pure orsubstantially free from impurities, as defined herein. In certain notlimiting embodiments, the resulting stream is at least about 99.5% pureHCFC-244bb with less than 5000 ppm of the impurities and the reactantfeed is ready for transfer to the dehydrohalogenation reactor.

The dehydrochlorination step can be carried out using one or more knownprocess techniques for conversion of HCFC-244bb to HFO-1234yf. To thisend, catalytic conversion of HCFC-244bb is conducted under anyconditions effective to dehydrochlorinate HCFC-244bb to produceHFO-1234yf. Preferably, though not exclusively, dehydrochlorination ofHCFC-244bb is done in a vapor phase, such as a fixed-bed reactor in thevapor phase. The dehydrohalogenation reaction may be conducted in anysuitable reaction vessel or reactor, but is preferably, though notexclusively, conducted in a reactor constructed from materials which areresistant to the corrosive effects of hydrogen chloride (to the extentthat such material is formed under the dehydrohalogenation conditions).Exemplified materials for such a reactor include, but are not limitedto, nickel and its alloys, including Hastelloy, Inconel, Incoloy, andMonel or vessels lined with fluoropolymers and may employ single ormultiple tubes packed with a dehydrohalogenation catalyst.

The catalysts for the dehydrohalogenation reaction may include metalhalides, halogenated metal oxides, neutral (or zero oxidation state)metal or metal alloy, or activated carbon in bulk or supported form.When metal halides or metal oxides catalysts are used, preferably mono-,bi-, and tri-valent metal halides, oxide and theirmixtures/combinations, and more preferably mono-, and bi-valent metalhalides and their mixtures/combinations. Component metals include, butare not limited to, Cr³⁺, Fe³⁺, Mg²⁺, Ca²⁺, Ni²⁺, Zn²⁺, Pd²⁺, Li²⁺,Na²⁺, K²⁺, and Cs². Component halogens include, but are not limited to,F⁻, Cl⁻, Br⁻, and I⁻. Examples of useful mono- or bi-valent metal halideinclude, but are not limited to, LiF, NaF, KF, CsF, MgF₂, CaF₂, LiCl,NaCl, KCl, and CsCl. Halogenation treatments can include any of thoseknown in the prior art, particularly those that employ HF, F₂, HCl, Cl₂,HBr, Br₂, HI, and I₂ as the halogenation source.

When neutral, i.e., zero valent, metals, metal alloys and their mixturesare used. Useful metals include, but are not limited to, Pd, Pt, Rh, Fe,Co, Ni, Cu, Mo, Cr, Mn, and combinations of the foregoing as alloys ormixtures. The catalyst may be supported or unsupported. Useful examplesof metal alloys include, but are not limited to, SS 316, Monel 400,Inconel 825, Inconel 600, and Inconel 625.

The HCFC-244bb is introduced into the reactor either in pure form,partially purified form, or as part of the reactor effluent from thepreceding step. The HCFC-244bb may optionally be fed with an inert gasdiluent such as nitrogen, argon, or the like. In a preferred, thoughnon-exclusive, embodiment of the invention, the HCFC-244bb ispre-vaporized or preheated prior to entering the reactor. Alternately,the HCFC-244bb is vaporized inside the reactor.

Useful reaction temperatures may range from about 100° C. to about 700°C. Preferred temperatures may range from about 150° C. to about 600° C.,and more preferred temperatures may range from about 200° C. to about550° C. The reaction may be conducted at atmospheric pressure,super-atmospheric pressure or under vacuum. The vacuum pressure can befrom about 5 torr (0.0966 psia) to about 760 torr (14.69 psia). Contacttime of the HCFC-244bb with the catalyst may range from about 0.5seconds to about 120 seconds, however, longer or shorter times can beused.

In such dehydrochlorination embodiments, the conversion of theHCFC-244bb is at least about 10%, more preferably at least about 20%,and even more preferably at least about 30%. Preferably in suchembodiments, the selectivity to HFO-1234yf, is at least about 70%, morepreferably at least about 85% and more preferably at least about 95%.

In certain embodiments, the process flow is in the down or up directionthrough a bed of the catalyst. It may also be advantageous toperiodically regenerate the catalyst after prolonged use while in placein the reactor. Regeneration of the catalyst may be accomplished by anymeans known in the art such as using an oxidizing agent such as O₂ orchlorine. For example, by passing air or air diluted with nitrogen overthe catalyst at temperatures of from about 100° C. to about 400° C.,preferably from about 200° C. to about 375° C., for from about 0.5 hourto about 3 days depending on the size of the reactor.

In general, the effluent from the dehydrohalogenation reaction step,including any intermediate effluents that may be present in multi-stagereactor arrangements, may be processed to achieve desired degrees ofseparation and/or other processing. For example, in embodiments in whichthe reactor effluent comprises HFO-1234yf, the effluent will generallyalso include HCl and unreacted HCFC-244bb. Some portion or substantiallyall of these components of the reaction product may be recovered fromthe reaction mixture via any separation or purification method known inthe art such as neutralization and distillation. It is expected thatunreacted HCFC-244bb could be recycled, completely or partially, toimprove the overall yield of the desired CF₃CF═CH₂ (HFO-1234yf).Optionally but preferably, hydrogen chloride is then recovered from theresult of the dehydrochlorination reaction. Recovering of hydrogenchloride is conducted by conventional distillation where it is removedfrom the distillate.

Alternatively, HCl can be recovered or removed by using water or causticscrubbers. When a water extractor is used HCl is removed as an aqueoussolution. When caustic is used, HCl is just removed from system as achloride salt in aqueous solution.

The following are examples of the invention and are not to be construedas limiting.

EXAMPLES Example 1

This example illustrates the continuous liquid phase fluorinationreaction of 2-chloro-3,3,3-trifluoropropene(HCFO-1233xf)+HF→2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb). Thefluorination catalyst for the experiment was SbCl₅.

About 5618 grams of SbCl₅ were contained in a Teflon™-lined liquid phasereactor equipped with a 2-inch ID (inside diameter) packed column and acondenser. The reactor was 2.75-inch ID×36-inch L (length). Initially, agreater than 5:1 mole ratio of HF was added to the reactor to fluorinatethe catalyst. A greater than 3:1 mole ratio of Cl₂ was then added to thereactor to ensure that the catalyst was brought back to a pentavalentstate. The reactor was heated to about 85° C.-87° C. HF feed was startedfirst. When an additional 1.5 lbs of HF had been added the2-chloro-3,3,3-trifluoropropene feed was started. The purity of the2-chloro-3,3,3-trifluoropropene feed stock was about 97.3 GC (gaschromatograph) area %. The experiment ran continuously for about 162hours. For this run, chlorine was fed batchwise about every 4 hoursthroughout the run to keep the catalyst active.

Conversion was immediately above 98%, and remained that way throughoutthe rest of the run. The average feed rates of HF and HCFO-1233xf were0.91 and 0.88 lb/hr respectively. The chlorine additions amounted toabout 3.0% by weight of the average organic feed rate. About 123 poundsof acid-free 2-chloro-1,1,1,2-tetrafluoropropane crude were collected.

The reactor temperature range for the experiments was 78° C.-86° C. andthe pressure range was 70 psig-105 psig. The reaction was monitored bysampling the reactor effluent stream periodically. The samples wereanalyzed on a gas chromatograph. The average conversion of2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) of about 98% and thefollowing average product selectivity: HCFC-244bb=90%, HCFO-1223xd=1%and HFC-245cb=8%.

Example 2

This example illustrates the difficulty in obtaining high purity 244bbusing a conventional batch distillation column

The crude HCFC-244bb produced in a reaction run similar to thatdescribed in Example 1 was continuously fed into a caustic scrubber toremove unreacted HF and HCl by-product (formed during impurityformation). Then the product stream was passed through a column filledwith desiccant to remove residual moisture and collected. 100 lbs ofthis material was charged to a distillation column consisting of a 10gallon reboiler, 2 inch ID by 10 foot column packed with ¼″ Propakpacking, and a shell and tube heat exchanger for a condenser. The columnhad about 30 theoretical plates. The distillation column was equippedwith temperature, pressure, and differential pressure transmitters. Thedistillation was run at 27 psig pressure and D/P in the range of 13-15inches of H2O. The composition of the material charged to thedistillation column was 3.85 GC area % HFC-245cb, 91.2 GC area %HCFC-244bb, 2.46 GC area % HCFO-1233xf, 1.1% GC area % HCFO-1223xd, and1.4 GC area % including HCFO-1232xf.HFO-1243zf, chlorotetrachloropropeneisomers, HCFO-1223zd, HFO-1234ze, HFO-1225ye, HFC-254eb, HFC-2541b, and3,3,3-trifluoropropyne, among others. Only 40 lbs of 99.25 GC area %HCFC-244bb was recovered from the distillation. Impurities included1233xf, chlorotetrafluoropropenes, 1233zd, 1223xd, and 1243zf.Additionally, 46 lbs of 94 GC area % HCFC-244bb and 5 GC area %HCFO-1233xf mixture was recovered and contained the same impurities asabove with the addition of 245cb and 3,3,3-trifluoropropyne.

Example 3

The 99.25 GC area % HCFC-244bb recovered in Example 2 was used as feedto a reactor containing a dehydrochlorination catalyst. The reaction washighly selective to HFO-1234yf and a crude HFO-1234yf product thatcontained<1.0 GC area % impurities other than unconverted HCFC-244bb wasproduced. Using relatively pure HCFC-244bb as a feed to thedehydrochlorination reaction also improved dehydrochlorination catalyststability. Catalyst stability was constant for over 1000 hours ofcontinuous run time as compared to <500 hours using unpurified 244bbfeed.

Example 4

A crude HCFC-244bb stream composed of 3.85 GC area % HFC-245cb, 91.2 GCarea % HCFC-244bb, 2.46 GC area % HCFO-1233xf, 1.1% GC area %HCFO-1223xd, and 1.4 GC area % others including HCFO-1232xf, HFO-1243zf, chlorotetrachloropropene isomers, HCFO-1223zd, HFO-1234ze, HFO-1225ye,HFC-254eb, HFC-2541b, and 3,3,3-trifluoropropyne among others is chargedinto a jacketed photochlorination reactor where a 450 watt ultravioletlight source is present and turned on. A stream of C12 is sparged intothe photochlorination reactor where it adds across the double bonds ofunsaturated impurities, especially 3,3,3-trifluoropropyne, HCFO-1233xf,HFO-1243zf and HCFO-1223xd producing high boiling products easilyseparated by conventional distillation. Cl₂ is added in a 20% excess tothe stoichiometric amount needed to convert all the unsaturatedcompounds in the crude material. The reactor is run at near atmosphericpressure (0-10 psig) and the contents are cooled using circulatingchilled brine through the reactor jacket. The reaction time is about 2to about 4 hours. Regular sampling and subsequent GC analysis of thereactor contents confirms when the chlorination reaction is complete. Aslightly caustic solution containing the amount of bisulfite required toneutralize unreacted chlorine in the reactor is added to a mixing tank.The amount of bisulfite used in the solution is about 0.015 weightpercent and the amount of sodium hydroxide used in the solution is about0.2%. The reaction mixture stream exits the photochlorination reactorand is added on top of the slightly caustic bisulfite solution in themixing tank. The contents of mixing tank are well mixed by means of anagitator and any excess Cl₂ or hydrochloric acid (by-product of Cl₂addition to saturated compounds) are neutralized by the bisulfite andcaustic, respectively.

After mixing, the agitator is shut off and the contents of mixing tankare allowed to phase separate into an upper aqueous phase and a lowercrude HCFC-244bb phase. The crude HCFC-244bb phase is then removed fromthe bottom of the mixing tank. After removal of the crude HCFC-244bbphase, the aqueous phase is removed for treatment. Then the acid and Cl₂free crude HCFC-244bb stream enters a drying column where any residualor dissolved water is removed by a desiccant.

The dried crude HCFC-244bb exiting the drying column enters aconventional distillation column for separation of2-chloro-1,1,1,2-tetrafluoropropane from impurities. Low boilingimpurities such as HFC-245cb are removed first followed by a greaterthan 99.8 weight percent 2-chloro-1,1,1,2-tetrafluoropropane streamcontaining less than 500 ppm of unsaturated halogenated hydrocarbons.

Example 5

This example illustrates the continuous vapor phase hydrogenationreaction of crude HCFC-244bb to convert unsaturated impurities tosaturated halocarbons that are easily separated from HCFC-244bb by anymeans known in the art such as distillation. Hydrogenation is performedusing Monel reactor (ID 0.5 inches, length 32 inches) equipped with avaporizer and preheater (ID 1 inch, length 32 inches) which is filledwith Nickel mesh to enhance heat transfer. The reactor is filled with 50milliliters of 1 wt %Pd/Al₂O₃ hydrogenation catalyst. Nickel mesh isplaced at the top and at the bottom of reactor to support the catalyst.A multi-point thermocouple is inserted at the center of the reactor. Acrude HCFC-244bb stream composed of 3.85 GC area % HFC-245cb, 91.2 GCarea % HCFC-244bb, 2.46 GC area % HCFO-1233xf, 1.1% GC area % 1223xd,and 1.4 GC area % others including HCFO-1232xf, HFO-1243zf,chlorotetrachloropropene isomers, HCFO-1223zd, HFO-1234ze, HFO-1225ye,HFC-254eb, HFC-2541b, and 3,3,3-trifluoropropyne among others isvaporized and fed at the rate 1 lb/hr. Hydrogen is co-fed at a rateresulting in 20-80 mol % excess to the stoichiometric amount required tocompletely hydrogenate unsaturated impurities present in the crudeHCFC-244bb feed. Hydrogen adds across the double bonds of unsaturatedimpurities, especially 3,3,3-trifluoropropyne, HCFO-1232xf, HCFO-1233xf,HFO-1243zf. HCFO-1223xd chlorotetrachloropropene isomers, HCFO-1223zd,HFO-1234ze and HFO-1225ye, producing both low- and high-boiling productsthat are easily separated from HCFC-244bb by conventional distillation.The reactor is heated to 200° C. by means of electric furnace. Reactionis run at the pressure about 45 psia.

The hydrogenated crude HCFC-244bb is charged to a conventional batchdistillation column for separation of2-chloro-1,1,1,2-tetrafluoropropane from impurities. Low boilingimpurities such as HFC-245cb (−18° C.) and 2631fb (BP −13° C.) areremoved first followed by a greater than 99.8 weight percent2-chloro-1,1,1,2-tetrafluoropropane distillate stream containing lessthan 500 ppm of unsaturated halogenated hydrocarbons.

Example 6

This example illustrates the negative effect of impurities in the 244bbfeed material on the stability of a MgF₂ based dehydrohalogenationcatalyst

A cylindrical Monel reactor of ¾″ diameter immersed into a 3-zoneelectrical furnace was used. Process temperatures were recorded using amulti-point thermocouple placed inside the reactor and within thecatalyst bed. The distance between two adjacent probe points was 4″. Thecatalyst was loaded in such a way that its bed was within two adjacentprobe points. 244bb was fed into the bottom of the vertically mountedreactor and was vaporized before reaching catalyst bed. Effluent gaseswere passed through a gas sampling tube and the progress of the reactionwas monitored periodically via GC analysis of the contents of the gassampling tube. 20 ml of catalyst was charged and the flow rate oforganic was 6 g/h in a typical run. As shown in FIG. 1, with89.7%244bb/7.3%1233xf/3% others feed, 244bb conversion was decreasedfrom above 50% initially to below 40% after only 24 hours on stream. Theimpurities in the feed caused premature deactivation of thedehydrochlorination catalyst.

Comparative Example 6

This comparative example shows that using a relatively pure 244bb feedmaterial has a positive effect on the stability of a MgF2 baseddehydrohalogenation catalyst. The same set-up and reaction conditionsthat were used in Example 6 were used. The 244bb feed material was 99.0%pure with the major impurity being 1233xf at 0.8%. The catalyst FIG. 2shows that the dehydrochlorionation catalyst is stable for over 450hours of on-stream time.

Example 7

This example illustrates the highly selective 244bb dehydrochlorinationreaction to produce 1234yf in Inconel 625 reactor.

A cylindrical Inconel 625 reactor of ¾″ diameter immersed into a 3-zoneelectrical furnace was used. Process temperatures were recorded using amulti-point thermocouple placed inside the reactor. The 244bb feedmaterial was of 99.37 GC area % purity and contained some unsaturatedimpurities with the major impurity being HCFO-1233xf at about 0.5 GCarea % and about 0.13% other unsaturated compounds. The material hadbeen purified by distillation only, which was not capable of removingcertain unsaturated compounds. 244bb was fed into the bottom of thevertically mounted reactor and was vaporized before reaching reactionzone. Effluent gases were passed through a gas sampling tube and theprogress of the reaction was monitored periodically via GC analysis ofthe contents of the gas sampling tube. As shown in FIG. 3, 244bbconversions at 480° C. and 25 psig were generally between 50 and 55%(52.5% on average) and no deactivation was noted during the period oftime of the test which lasted for about 1000 hours. The selectivity to1234yf remained high at around 99.8% during the reaction.

A gas-bag sample was taken at 480° C. and 25 psig and analyzed by meansof GC-MS. For comparison purpose, the feed was also analyzed. As shownin Table 1, other than trace amounts of C₁, C₂, and C₄ by-products,which were produced most likely through the breakage of 244bb and/orother molecules, no other by-products were formed during reaction. Inaddition, unsaturated species (such as 1233 and 1224) included infeedstock remained present in product stream, indicating no reactionoccurred to those unsaturated species during 244bb dehydrochlorinationin Inconel 625 reactor.

TABLE 1 GC-MS analysis of products formed from 244bb dehydrohalogenationin Inconel 625 reactor Species Identified Peak # Raw material Productsformed at 480° C.¹ 1 G23 2 134a 3 1234yf 4 HCl 5 347 6 244bb 244bb 7142b 142b 8 1224 1224 9 1233xf 1233xf 10 1224 1224 11 1233zd 1233zd 121224 iso 1224 iso 13 142 14 G30 ¹Other reaction conditions: ~25 psig, 12g-organic/h, and 99.4 GC area % 244bb/0.4 GC area % 1233xf

Example 8

This example illustrates the difficulty in obtaining high purity 1234yfusing a continuous conventional distillation column and 1234yf crudematerial produced from a 244bb feedstock containing >8% impuritiesincluding 3.85 GC area % HFC-245cb, 2.46 GC area % HCFO-1233xf, 1.1% GCarea % 1223xd, and 1.4 GC area % others including HCFO-1232xf,HFO-1243zf, chlorotetrachloropropene isomers, HCFO-1223zd, HFO-1234ze,HFO-1225ye, HFC-254eb, 254fb, and 3,3,3-trifluoropropyne, among others.The crude HFO-1234yf produced in was continuously fed into a causticscrubber to remove HCl by-product. Then the product stream was passedthrough a column filled with desiccant to remove residual moisture. Anoil-less compressor was used to feed crude product into the distillationcolumn that was maintained at 30-45 psig pressure. The distillationcolumn consisted of a 10 gallon reboiler, 2 inch ID by 10 foot columnpacked with ¼″ Propak packing , and a shell and tube heat exchanger fora condenser. The column had about 30 theoretical plates. Thedistillation column was equipped with temperature, pressure, anddifferential pressure transmitters. Distillation was performed in acontinuous mode and the take-off rate was equal to the rate ofproduction of HFO-1234yf in the reactor. The purity of distilledHFO-1234yf was only 99.0 GC area %. GC analysis of the distillate showedthe presence of both lower boiling and higher boiling impuritiesincluding 3,3,3-trifluoropropyne, HFO-1243zf, chlorotetrachloropropeneisomers, HCFO-1223zd, HFO-1234ze, HFC-245cb, HCFO-1233xf, andHCFC-244bb. HCFO-1223xd and HCFO-1232xf were not detected. The bottomsof the distillation column were discharged and recycled into thedehydrochlorination reactor.

Example 9

The distillation overhead material collected from the continuousdistillation in Example 7 needed to be further purified by batchdistillation to meet an internal Honeywell 1234yf product specification.The same distillation equipment described in Example 7 was used, but runin batch mode. The batch distillation was done at 50 psig pressure andD/P in the range of 20-35 inches of H₂O meaning the separation requireda huge reflux stream. The starting purity of HFO-1234yf was about 99GC%. Take off rate was 0.5 lb/hr for the light cut and 0.5-1.0 lb/hr forthe main cut. In both cases the light cut was about 7wt % of the initialamount of material charged into reboiler. 50 lb of material was chargedinto reboiler. Weight of light cut was 3.5 lb (light cut was collecteduntil the purity of HFO-1234yf exceeded 99.9%). The weight of the mainHFO-1234yf cut was 36.5 lb. The purity of HFO-1234yf in the main cut wasgreater than 99.96 GC %. Distillation was stopped due to low level inthe reboiler. Table 2 is the GC analysis of the purified HFO-1234yf.

TABLE 2 Summary of GC results for the sample of HFO-1234yf produced fromHCFC-244bb using CsCl/MgF2 catalyst and distilled twice. CompoundConcentration (wt %) HFO-1234yf 99.9671% Hexafluorobutyne 8 ppm R-245cb4 ppm R-134a 68 ppm 3,3,3-trifluoropropyne <1 ppm R-1243zf 198 ppmR-1234ze 11 ppm R-1113 3 ppm R-12 13 ppm R-1131 6 ppm R-1122a 3 ppmR-1140 7 ppm R-244bb 3 ppm R-1233xf <1 ppm Unknown 3 ppm Totalunsaturates (other than HFO-1234yf) - 237 ppm

What is claimed is:
 1. A method for purifying a composition containing2-chloro-1, 1,1, 2-tetrafluoropropane (244bb) comprising: providing acomposition comprising 2-chloro-1,1,1,2-tetrafluoropropane and at leastone unsaturated halogenated hydrocarbon impurity; saturating the atleast one unsaturated halogenated hydrocarbon impurity to produce asaturated halogenated hydrocarbon impurity; and separating the saturatedhalogenated hydrocarbon impurity from the2-chloro-1,1,1,2-tetrafluoropropane to produce a product containing lessthan 500 ppm of said saturated halogenated hydrocarbon impurity.
 2. Themethod of claim 1, wherein the saturating step comprises aphotochlorination reaction.
 3. The method of claim 1, wherein thesaturating step comprises a hydrogenation reaction.
 4. The method ofclaim 1, wherein the separating step comprises distillation.
 5. Themethod of claim 1, wherein the separating step comprises extraction.